Typically, notebook holders that let you put your computer on your lap while shielding your skin from the heat need to be larger than the laptop, which doesn't make them very convenient for travel. The $17 Laptop Lilo is a possible solution, as it's inflatable.

This laptop support has a structure that allows for ventilation and can be collapsed so you can tote it around conveniently. It can withstand temperatures up to 80 degrees, which is good enough unless you have a seriously overheating portable.